Calculating output inductance of a weld secondary

ABSTRACT

A welding-type system includes a welding-type power supply to output welding-type power, and a controller connected to the welding-type power supply. The controller is configured to set a value of a control variable of a control loop of the welding-type power supply, the control loop controlling the welding-type power. The controller is also configured to adjust the value of the control variable while monitoring the control loop. In response to detecting oscillation in the control loop, the controller is configured to determine a weld circuit inductance associated with a weld circuit of the welding-type system based on a relationship between the adjusted control variable value and the weld circuit inductance.

BACKGROUND

Welding is a process that has become ubiquitous in various industriesand applications, such as construction, ship building, and so forth.Welding systems typically include a variety of secondary components,which may include secondary cabling as well as secondary equipment, andcertain parameters of these secondary components may impact the qualityof the weld obtained in a welding operation. For instance, certain workenvironments may position a welding location or workpiece largedistances from a welding power source. An inductance realized in asecondary component (e.g., a weld power cable) can adversely affect theoperation of the welding system. Thus, a system to calculate andmitigate such secondary inductance is desirable.

SUMMARY

Methods and systems are provided for calculating output inductance of aweld secondary, substantially as illustrated by and described inconnection with at least one of the figures, as set forth morecompletely in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example implementation of a weldingsystem in accordance with aspects of this disclosure.

FIG. 2 is a graphical diagram of experimental data from animplementation of the welding system of FIG. 1, in accordance withaspects of this disclosure.

FIG. 3 is another graphical diagram of experimental data from animplementation of the welding system of FIG. 1, in accordance withaspects of this disclosure.

FIG. 4 is a flowchart illustrating example machine readable instructionswhich may be executed by a processor to implement the controller of FIG.1 to determine a secondary inductance of a welding-type system.

DETAILED DESCRIPTION

Methods and systems are provided for calculating output inductance of asecondary weld cable configuration in a welding-type environment.Welding systems are configurable such that user controls (e.g.,software, hardware, or a combination of software and hardware) controlvoltage control loop variables (e.g., gain and/or feedback length) overa range of values, and employ the variables to calculate an outputinductance of a secondary component (e.g., a weld cable). Informationregarding the inductance of the secondary component can be significantin controlling welding processes, for example, in maintaining a suitableweld voltage at a welding-type torch in a welding-type environment.

Conventional systems determine the secondary inductance of a weldingsystem by relying upon measurements of voltage change during astep-change in the weld current during operation of the welding system.

Disclosed examples employ a method (e.g., a computer controlledalgorithm) to calibrate the system in a work environment. Avoltage-controlled (e.g., constant voltage, or CV) process can beselected (e.g., a short arc or “Accupulse” type process) and aproportional gain of the voltage-controlled system can be increaseduntil a control loop begins to oscillate in response. The system canidentify a gain value at which the oscillation begins and compare thegain value to a list of gain values that correspond to a list ofinductance values (e.g., calculated from previous, controlled tests) todetermine an inductance value that correlates to the identified gainvalue.

Disclosed examples employ another method to calibrate the system in awork environment. In this example, the proportional gain is fixed and aproportional filter length is reduced until oscillations began. Onceidentified, a filter length value is compared against a list of filterlengths that correspond to a list of known inductance values todetermine an inductance value that correlates to the identified filterlength value.

Disclosed examples employ a combination of the gain and filter lengthvalues to identify an inductance value.

Disclosed example welding-type systems include a welding-type powersupply to output welding-type power, and a controller connected to thewelding-type power supply. The controller is configured to set a valueof a control variable of a control loop of the welding-type powersupply, the control loop controlling the welding-type power. Thecontroller is also configured to adjust the value of the controlvariable while monitoring the control loop. In response to detectingoscillation in the control loop, the controller is configured todetermine a weld circuit inductance associated with a weld circuit ofthe welding-type system based on a relationship between the adjustedcontrol variable value and the weld circuit inductance.

In some examples, the control variable includes at least one of aproportional gain or a proportional filter length. In some examples, thecontrol variable is set at a predetermined value of the proportionalgain, and the controller is configured to increase the value of theproportional gain until the oscillation is detected in the control loop.In some examples, the controller is also configured to adjust theproportional gain to an optimized level between minimum and maximumproportional gain values. In some examples, the welding-type systemincludes a storage device storing a look up table that includes a listof proportional gain values and corresponding inductance values.

In some examples, the controller is further configured to compare theproportional gain value corresponding to the detected oscillation to thelist of proportional gain values, determine a proportional gain value inthe list of proportional gain values that substantially matches theproportional gain value corresponding to the detected oscillation, andidentify an inductance value corresponding to the proportional gainvalue as the secondary inductance of the weld circuit.

In some examples, the control circuit is configured to interpolate aninductance value based on two inductance values associated withcorresponding proportional gain values in the list of proportional gainvalues, the corresponding proportional gain values selected based on thevalue of the proportional gain when the oscillation is detected. In someexamples, the control variable is set at a predetermined value of theproportional filter length, the control circuit further configured todecrease the value of the filter length until the oscillation isdetected in the voltage control loop.

In some examples, the controller is configured to calculate an errorvalue based on a comparison of a feedback voltage to a predeterminedreference voltage, and determine a proportional change in the value ofthe control variable based on the error value. In some examples, thecontroller is configured to set a minimum value and a maximum value forthe proportional change to reduce the oscillation in the voltage controlloop. In some examples, the controller includes a filter configured tofilter the feedback voltage to increase a signal to noise ratio. In someexamples, the filter is configured to collect a number of feedbackvoltage samples, and calculate an average value of the feedback voltagesamples. In some examples, the control loop is one of a voltage controlloop and a current control loop.

Welding-type power, as used herein, refers to power suitable forwelding, plasma cutting, induction heating, air carbon-arc cuttingand/or gouging (CAC-A), cladding, and/or hot wire welding/preheating(including laser welding and laser cladding), including inverters,converters, choppers, resonant power supplies, quasi-resonant powersupplies, etc., as well as control circuitry and other ancillarycircuitry associated therewith.

In an example, output inductance is demonstrated by the behavior of acable (e.g., a coiled cable) in resisting a change of electric currentthrough the cable. The inductance may be defined in terms of theelectromotive force generated to oppose a change in current within thecable. When a change of current is experienced in a secondary weldingcomponent like a cable, the voltage can vary from output at the powersupply to the torch, resulting in an uncontrolled weld output. Thepresent disclosure provides systems and methods that determine theinductance of the cable, which allows the system to mitigate negativeimpacts from inductance introduced in the weld power cables, asdescribed in detail with respect to the figures.

FIG. 1 illustrates an example welding-type system 100 suitable forpowering welding operations. The welding-type system 100 includes awelding-type power supply 102, a device, such as welding type torch 106,a weld power cable 104, and a controller 110. The system 100 can alsoinclude a workpiece 108 and a volt sensing cable 109 to create acircuit, as shown in FIG. 1. The welding torch 104 may be a torchconfigured for stick welding, tungsten inert gas (TIG) welding, metalinert gas (MIG), gas metal arc welding (GMAW), or other torch types,based on the desired welding application. The system 100 may be coupledto other devices, such as a wire feeder, an induction heater, a plasmacutter, a power generator, or any combination thereof. The inductance ofthe weld power cable 104 may affect the power output provided from thepower supply 102 to the device. As discussed below, the system 100 isconfigured to determine the inductance of the weld power cables 104, aswell as the secondary device.

The example controller 110 of FIG. 1 controls the operations of thesystem 100 and may be a general-purpose computer, a laptop computer, atablet computer, a mobile device, a server, and/or any other type ofcomputing device integrated or remote to the system 100. In someexamples, the controller 110 is implemented in a cloud computingenvironment, on one or more physical machines, and/or on one or morevirtual machines. The controller 110 is in communication with one ormore interfaces 114, for example, an operator interface, a networkinterface, and an interface with a storage device 112.

The controller 110 may receive input from the one or more interfaces 114through which the welding type system receives commands from, forexample, an operator (e.g., a welder). In some examples, the operatormay employ one or more interfaces 114 to choose a welding process (e.g.,stick, TIG, MIG, etc.) and desired parameters of the input power (e.g.,voltages, currents, etc.). The controller 110 may be configured toreceive and process a plurality of inputs regarding the performance anddemands of the system 100. The storage device 112 may include volatileor non-volatile memory, such as ROM, RAM, magnetic storage memory,optical storage memory, or a combination thereof, and may be integratedwith the controller 110, located remotely, or a combination of the two.In addition, a variety of control parameters may be stored in thestorage device 112 along with code configured to provide a specificoutput during operation.

In a working environment, secondary components, such as the torch 106,are connected to the power supply 102 by the weld power cable 104 whichcan vary in length and introduce a secondary inductance. The controller110 executes a process employing one or more variables to determine aninduction of the secondary component (e.g., the weld power cable 104).The controller 110 compares the one or more variables against a list ofvalues stored in the storage device 112, which can then be used toadjust a welding parameter to ensure proper operation of the system 100.For example, the controller 110 may utilize a look up table, analgorithm, and/or a model stored in the storage device 112 to determinethe inductance of the weld power cable 104 based on a relationshipbetween the variables and the values stored in memory. The controller110 can then adjust a characteristic of the system 102 (e.g., an output)to mitigate effects of the inductance.

In an example, the system 100 is rated with a power output range, andhas an acceptable inductance range associated with welding-typeoperations. The welding-type torch 106 may be located a distance fromthe welding power supply 102 and connected by the weld power cable 104.For example, the welding power supply 102 may be in a differentbuilding, structure, or room than the power supply 102. The inductancemay vary during use as the weld power cables 104 are coiled, extended,and/or moved. Properties that affect the inductance of a weld powercable 104 may include length of the weld power cable 104, material ofconductors within the weld power cable 104, disposition of the weldpower cable 104 (e.g., coiled, straight), disposition relative toconductive materials (e.g., coiled around a rod), arrangement (e.g.,parallel, twisted) relative to other weld power cables, and proximity toinductive sources (e.g., other weld power cables).

The addition of the secondary inductance can cause disparities in theweld voltage between the torch 106 and the workpiece 108. In an exampleprocess to maintain a given variable and/or parameter at apre-determined, pre-set level, the controller 110 utilizes a controlloop. In the control loop, the variable to be maintained at the pre-setlevel is constantly monitored (e.g., sampled, measured, etc.) andcompared to a desired level. This monitoring is termed feedback.Differences, for example, positive or negative changes, revealed duringthe comparison between the desired level and the actual (i.e.instantaneous) feedback are determined as an error. The system andmethods described herein employ the measured and determined variablesand/or parameters to maintain the system operation at a pre-set level.

In an example MIG welding system, the variable to maintain at a pre-setlevel can be a process voltage. Real-time voltage is measured andsampled at a predetermined rate in order to receive a suitable feedbacksignal. For example, the system 100 can sample the voltage 50,000 timesper second, equating to 20 μsec between samples. Each time a sample ofthe voltage is taken, a calculation is performed to determine the error,as shown in equation 1:

ϵ=(V _(set) −V _(fbk))   Equation 1

Once an error term is calculated, the error is employed to restore thevoltage to a predetermined value. In an example, the error is positive,indicating that the actual, instantaneous voltage is less than thepredetermined value. Thus, the controller 110 adjusts the voltage toincrease the process voltage of the system 100 (e.g., the voltage at thewelding-type torch 106). In other examples welding systems, the controlvariable is a welding current.

A direct relationship exists between arc voltage and arc current in aconstant wire-feed speed (WFS) MIG process. Increasing the arc currentby a certain amount will therefore directly increase the processvoltage. In other words, when the error term is positive, the controller110 increases the control variable (e.g., current and/or voltage) inorder to raise the actual voltage to a value closer to the desiredvalue, thereby reducing the error term.

In order to determine by what magnitude the current is to be increasedto get the voltage to the desired value, the controller 110 adjusts thecurrent proportionally to the magnitude of the error term. This isexpressed mathematically, in Equation 2 as follows:

I _(command) =I _(nominal) +ϵ·P _(gain)   Equation 2

In Equation 2, I_(command) is the current command sent to the powersource, I_(nominal) is the average current level expected for the givenWFS (wire feed speed), ϵ is the voltage error term calculated fromEquation 1, P_(gain) is the gain value for the proportional control thatdetermines how many amps/volt change to produce for a given voltageerror (P_(gain) is represented by parameters “Arc Proportional Gain” forthe arc phase and “Short Proportional Gain” for the short phase). Theallowable range of these parameters lies between the “P-gain Min” and“P-gain Max” parameter settings.

Since sampling of the voltage feedback is done at a high rate (e.g.,50,000 times per second) it is not necessary or beneficial to adjustcurrent in response to each sample. Moreover, in an electromagneticallynoisy environment, random noise signals can be superimposed on themeasured process voltage feedback. Overreacting to such noise wouldadversely affect the process stability. To avoid unnecessary adjustment,the controller 110 filters the V_(fbk) signal. In this manner, thecontroller 110 can perform a running average of the V_(fbk) samples overa predetermined number of samples.

FIG. 2 illustrates a solid line as a voltage waveform from a weldoperation and a dashed line is the same data generated from a runningaverage of 4 sampled data points. The noise spike at about 4.01 secondsis significantly reduced in amplitude by the filter so that thecorresponding change to the current command will be less, therebyensuring adjustments are made deliberately within a suitable timeframe.

Setting the proportional filter requires more than selecting a number ofdata points to include in the running average. The proportional filterdoes not react directly to the voltage feedback signal values; ratherthe proportional filter is used to filter the error between the V_(set)and V_(fbk) values. As explained above, each time a voltage sample istaken, an error term is calculated, as shown in Equation 3:

ϵ_(i)=(V _(set) −V _(fbk) _(i) )   Equation 3

As shown in Equation 3, the “i” subscript identifies the most recentlyacquired V_(fbk) sample. To achieve filtering of the error, a runningaverage of a predetermined number of values of the error term iscalculated. This running average is the sum of the last N values of theerror term divided by N. Equation 4 shows an example when N=4:

$\begin{matrix}{ɛ_{p\_ {avg}} = \frac{ɛ_{i - 3} + ɛ_{i - 2} + ɛ_{i - 1} + ɛ_{i}}{N}} & {{Equation}\mspace{14mu} 4}\end{matrix}$

To avoid storing each of the last sample in memory for a very longsampling, and thereby reducing the amount of computational powerdedicated to calculating the error, a portion of the present value ofthe ϵ_(sum) is determined based on the size of the filter length N.Using the example of Equation 4 (e.g., N=4), the processor would firstsubtract off ¼ of the previous value of ϵ_(Psum) from itself. Inessence, the number of error samples has been reduced by 25%. Then, thesame percentage of the current error term ϵ_(i) is added back intoϵ_(Psum) _(new) . In this way, the results of the running averagecalculation are substantially reproduced and the computations aregreatly simplified.

FIG. 3 illustrates the same section of the voltage waveform shown inFIG. 2 with the running average filter and the digital filtering methodused by the controller 110. In FIG. 3, the proportional filter can bewithin the range of 0-16384. To achieve a filter value of N so that 1/Nof the ϵ_(Psum) _(old) is subtracted and 1/N of the ϵ_(i) is added eachtime the proportional error is recalculated, the conversion fromEquation 5 applies:

$\begin{matrix}{\frac{1}{N} = \frac{PropFilterValue}{16384}} & {{Equation}\mspace{14mu} 5}\end{matrix}$

Equation 6 provides a filter value for a desired filter length of 4:

PropFilterValue=4/16384 =4096   Equation 6

In order to increase the filter number, the controller 110 decreases thevalue of the proportional filter. One thing that is observed from thefiltered curves in FIGS. 2 and 3 is that the filtering introduces adelay in the voltage signal when a large step change occurs in thefeedback variable. This phenomenon is more pronounced as the filterlength increases.

FIG. 4 is a flowchart illustrating example machine readable instructions400 which may be executed by a processor (e.g., controller 110 ofFIG. 1) to calculate output inductance of a weld secondary (e.g., fromweld power cables 104) between a power supply (e.g., power supply 102)and a device (e.g., torch 106) of a welding-type system (e.g., system100). The example instructions 400 may be stored on the any suitablenon-transitory machine readable media, such as storage device 112described with respect to FIG. 1. At block 402, the controller sets avalue of a control variable of a voltage control loop, with the controlvariable including a proportional gain and/or a proportional filterlength. At block 404, the controller adjusts the value of the controlvariable while monitoring the voltage control loop. For example, thecontroller can increase the value of the proportional gain until theoscillation is detected in the voltage control loop. At block 406, thecontroller determines whether an oscillation is detected in the voltagecontrol loop. If no oscillation is detected, the controller continues tomonitor the voltage control loop, and returns to block 404. Ifoscillation is detected in the voltage control loop, the controllercontinues to block 408.

At block 408, the controller determines a secondary inductance of thewelding-type system based on a relationship between the control variableand the secondary inductance in response to detecting oscillation in thevoltage control loop. For example, the controller 110 is configured toaccess a storage device storing a look up table that includes a list ofproportional gain values and corresponding inductance values. Thecontroller 110 is further configured to compare an increased value ofthe proportional gain to the list of proportional gain values and, basedon the comparison, the controller 110 is configured to determine aproportional gain value in the list of proportional gain values thatsubstantially matches the increased value of the proportional gain, aswell as identify an inductance value corresponding to the proportionalgain value as the secondary inductance of the welding-type system. Inresponse, the controller 110 is configured to set a minimum value and amaximum value for a proportional change to reduce oscillation in thevoltage control loop. For example, the controller can adjust a currentof the welding-type power proportional to the increase in the value ofthe proportional gain.

In some examples, the controller 110 determines whether the inductancevalue is greater than a threshold inductance. The threshold inductancemay be a value input by the user and/or a value stored in a memory. Forexample, the device may be configured to reduce or eliminate the effectsof the secondary inductance when the inductance value is less than thethreshold inductance value. If the secondary inductance is greater thanthe threshold inductance value, the welding system 100 may signal (e.g.,via a display, sound, light, etc.) that the determined inductance of theweld cables 108 is greater than the threshold inductance.

The present methods and systems may be realized in hardware, software,and/or a combination of hardware and software. The present methodsand/or systems may be realized in a centralized fashion in at least onecomputing system, or in a distributed fashion where different elementsare spread across several interconnected computing systems. Any kind ofcomputing system or other apparatus adapted for carrying out the methodsdescribed herein is suited. A typical combination of hardware andsoftware may include a general-purpose computing system with a programor other code that, when being loaded and executed, controls thecomputing system such that it carries out the methods described herein.Another typical implementation may comprise one or more applicationspecific integrated circuit or chip. Some implementations may comprise anon-transitory machine-readable (e.g., computer readable) medium (e.g.,FLASH memory, optical disk, magnetic storage disk, or the like) havingstored thereon one or more lines of code executable by a machine,thereby causing the machine to perform processes as described herein. Asused herein, the term “non-transitory machine-readable medium” isdefined to include all types of machine readable storage media and toexclude propagating signals.

As utilized herein the terms “circuits” and “circuitry” refer tophysical electronic components (i.e. hardware) and any software and/orfirmware (“code”) which may configure the hardware, be executed by thehardware, and or otherwise be associated with the hardware. As usedherein, for example, a particular processor and memory may comprise afirst “circuit” when executing a first one or more lines of code and maycomprise a second “circuit” when executing a second one or more lines ofcode. As utilized herein, “and/or” means any one or more of the items inthe list joined by “and/or”. As an example, “x and/or y” means anyelement of the three-element set {(x), (y), (x, y)}. In other words, “xand/or y” means “one or both of x and y”. As another example, “x, y,and/or z” means any element of the seven-element set {(x), (y), (z), (x,y), (x, z), (y, z), (x, y, z)}. In other words, “x, y and/or z” means“one or more of x, y and z”. As utilized herein, the term “exemplary”means serving as a non-limiting example, instance, or illustration. Asutilized herein, the terms “e.g.,” and “for example” set off lists ofone or more non-limiting examples, instances, or illustrations. Asutilized herein, circuitry is “operable” to perform a function wheneverthe circuitry comprises the necessary hardware and code (if any isnecessary) to perform the function, regardless of whether performance ofthe function is disabled or not enabled (e.g., by a user-configurablesetting, factory trim, etc.).

The present methods and/or systems may be realized in hardware,software, or a combination of hardware and software. The present methodsand/or systems may be realized in a centralized fashion in at least onecomputing system, or in a distributed fashion where different elementsare spread across several interconnected computing systems. Any kind ofcomputing system or other apparatus adapted for carrying out the methodsdescribed herein is suited. A typical combination of hardware andsoftware may be a general-purpose computing system with a program orother code that, when being loaded and executed, controls the computingsystem such that it carries out the methods described herein. Anothertypical implementation may comprise an application specific integratedcircuit or chip. Some implementations may comprise a non-transitorymachine-readable (e.g., computer readable) medium (e.g., FLASH drive,optical disk, magnetic storage disk, or the like) having stored thereonone or more lines of code executable by a machine, thereby causing themachine to perform processes as described herein.

While the present method and/or system has been described with referenceto certain implementations, it will be understood by those skilled inthe art that various changes may be made and equivalents may besubstituted without departing from the scope of the present methodand/or system. In addition, many modifications may be made to adapt aparticular situation or material to the teachings of the presentdisclosure without departing from its scope. Therefore, the presentmethod and/or system are not limited to the particular implementationsdisclosed. Instead, the present method and/or system will include allimplementations falling within the scope of the appended claims, bothliterally and under the doctrine of equivalents.

What is claimed is:
 1. A welding-type system, comprising: a welding-typepower supply to output welding-type power; a controller connected to thewelding-type power supply configured to: set a value of a controlvariable of a control loop of the welding-type power supply, the controlloop controlling the welding-type power; adjust the value of the controlvariable while monitoring the control loop; and in response to detectingoscillation in the control loop, determine a weld circuit inductanceassociated with a weld circuit of the welding-type system based on arelationship between the adjusted control variable value and the weldcircuit inductance.
 2. The welding-type system as defined in claim 1,wherein the control variable comprises at least one of a proportionalgain or a proportional filter length.
 3. The welding-type system asdefined in claim 2, wherein the control variable is set at apredetermined value of the proportional gain, the controller configuredto increase the value of the proportional gain until the oscillation isdetected in the control loop.
 4. The welding-type system as defined inclaim 3, the controller further configured to adjust the proportionalgain to an optimized level between minimum and maximum proportional gainvalues.
 5. The welding-type system as defined in claim 3, furthercomprising a storage device storing a look up table that includes a listof proportional gain values and corresponding inductance values.
 6. Thewelding-type system as defined in claim 5, wherein the controller isfurther configured to: compare the proportional gain value correspondingto the detected oscillation to the list of proportional gain values;determine a proportional gain value in the list of proportional gainvalues that substantially matches the proportional gain valuecorresponding to the detected oscillation; and identify an inductancevalue corresponding to the proportional gain value as the secondaryinductance of the weld circuit.
 7. The welding-type system as defined inclaim 6, wherein the control circuit is configured to interpolate aninductance value based on two inductance values associated withcorresponding proportional gain values in the list of proportional gainvalues, the corresponding proportional gain values selected based on thevalue of the proportional gain when the oscillation is detected.
 8. Thewelding-type system as defined in claim 2, wherein the control variableis set at a predetermined value of the proportional filter length, thecontrol circuit further configured to decrease the value of the filterlength until the oscillation is detected in the voltage control loop. 9.The welding-type system as defined in claim 1, wherein the controller isconfigured to: calculate an error value based on a comparison of afeedback voltage to a predetermined reference voltage; and determine aproportional change in the value of the control variable based on theerror value.
 10. The welding-type system as defined in claim 9, whereinthe controller is configured to set a minimum value and a maximum valuefor the proportional change to reduce the oscillation in the voltagecontrol loop.
 11. The welding-type system as defined in claim 9, whereinthe filter is configured to: collect a number of feedback voltagesamples; and calculate an average value of the feedback voltage samples.12. The welding-type system as defined in claim 1, wherein the controlloop is a voltage control loop.
 13. The welding-type system as definedin claim 1, wherein the control loop is a current control loop.
 14. Anon-transitory machine readable storage device comprising machinereadable instructions which, when executed, cause a controller to: set avalue of a control variable of a control loop of a welding-type powersupply in a welding-type system; adjust the value of the controlvariable while monitoring the control loop; and determine a secondaryinductance of the welding-type system based on a relationship betweenthe control variable and the secondary inductance in response todetecting oscillation in the control loop.
 15. The non-transitorymachine readable storage device as defined in claim 14, wherein thecontrol variable comprises at least one of a proportional gain and aproportional filter length.
 16. The non-transitory machine readablestorage device as defined in claim 15, wherein the control variable isset at a predetermined value of the proportional gain, the instructionsto cause the controller to increase the value of the proportional gainuntil the oscillation is detected in the control loop.
 17. Thenon-transitory machine readable storage device as defined in claim 16,wherein the instructions, when executed, cause the controller to adjusta current of the welding-type power proportional to the increase in thevalue of the proportional gain.
 18. The non-transitory machine readablestorage device as defined in claim 17, wherein the instructions, whenexecuted, cause the controller to access a second storage device storinga look up table that includes a list of proportional gain values andcorresponding inductance values.
 19. The non-transitory machine readablestorage device as defined in claim 15, wherein the control variable isset at a predetermined value of the proportional gain, the instructionsto cause the controller to decrease the value of the proportional gainuntil the oscillation is no longer detected in the control loop.
 20. Thenon-transitory machine readable storage device as defined in claim 18,wherein the instructions, when executed, cause the controller to:compare an increased value of the proportional gain to the list ofproportional gain values; determine a proportional gain value in thelist of proportional gain values that substantially matches theincreased value of the proportional gain; and identify an inductancevalue corresponding to the proportional gain value as the secondaryinductance of the welding-type system.